全文获取类型
收费全文 | 8114篇 |
免费 | 1199篇 |
国内免费 | 567篇 |
专业分类
电工技术 | 482篇 |
综合类 | 705篇 |
化学工业 | 1112篇 |
金属工艺 | 324篇 |
机械仪表 | 443篇 |
建筑科学 | 735篇 |
矿业工程 | 236篇 |
能源动力 | 237篇 |
轻工业 | 618篇 |
水利工程 | 237篇 |
石油天然气 | 233篇 |
武器工业 | 131篇 |
无线电 | 1203篇 |
一般工业技术 | 603篇 |
冶金工业 | 418篇 |
原子能技术 | 548篇 |
自动化技术 | 1615篇 |
出版年
2024年 | 16篇 |
2023年 | 87篇 |
2022年 | 180篇 |
2021年 | 217篇 |
2020年 | 232篇 |
2019年 | 263篇 |
2018年 | 263篇 |
2017年 | 300篇 |
2016年 | 394篇 |
2015年 | 419篇 |
2014年 | 561篇 |
2013年 | 819篇 |
2012年 | 596篇 |
2011年 | 623篇 |
2010年 | 482篇 |
2009年 | 538篇 |
2008年 | 484篇 |
2007年 | 493篇 |
2006年 | 431篇 |
2005年 | 391篇 |
2004年 | 312篇 |
2003年 | 293篇 |
2002年 | 266篇 |
2001年 | 231篇 |
2000年 | 192篇 |
1999年 | 165篇 |
1998年 | 116篇 |
1997年 | 95篇 |
1996年 | 72篇 |
1995年 | 68篇 |
1994年 | 39篇 |
1993年 | 28篇 |
1992年 | 30篇 |
1991年 | 22篇 |
1990年 | 25篇 |
1989年 | 18篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1966年 | 4篇 |
1964年 | 6篇 |
1961年 | 5篇 |
1959年 | 8篇 |
1957年 | 5篇 |
1956年 | 4篇 |
排序方式: 共有9880条查询结果,搜索用时 222 毫秒
21.
Polarity Effect and Electromagnetic Radiation of Partial Discharge Accompanying Growth of Electrical Tree 下载免费PDF全文
Tatsuya Mutakamihigashi Yoshito Kuroishi Hideki Ueno 《Electrical Engineering in Japan》2015,192(3):19-26
We have investigated the characteristics of radiated electromagnetic (EM) waves from positive and negative partial discharges (PD) in epoxy resin and cross‐linked polyethylene. We found that there is a correlation among the EM level from PD, the positive PD current, and electrical trees. Therefore, the growth of an electrical tree produces a lot of positive PD. We have also investigated the characteristics of the frequency region of EM waves from PD in air, insulating oil, and liquid epoxy in addition to the above insulators. EM waves were detected in the frequency region of 40 MHz to 300 MHz from positive and negative PD in epoxy resin and cross‐linked polyethylene. EM waves were also detected in the frequency region of 40 MHz to 150 MHz from positive and negative PD in air. In the case of insulating oil and liquid epoxy, EM waves were detected in the frequency regions of 40 MHz to 150 MHz from positive PD, and 40 MHz to 250 MHz from negative PD. The frequency region differed depending on the material and the discharge polarity. Our investigation indicates that the cause is differences in electric field strength at the time of PD occurrence. 相似文献
22.
针对高集成度射频收发器(AD9361)实现差分正交调制解调(DQPSK)收发过程中存在的工程实现问题,采用理论分析与硬件平台实现相结合的方法测试AD9361,验证DQPSK调制解调;先通过Serial Peripheral Interface(SPI)接口测试AD9361自发自收,采用点积叉积方法实现了DQPSK的调制解调;配置AD9361过程中,通过测试定位初始化后AD9361输出端无波形、通过示波器观察发现AD9361发射与接收本振时域波形扭曲、频谱仪观察AD9361输出端谐波分量严重、DQPSK解调时发射本振与接收本振存在随机相位误差4个疑难问题,分别通过采用降低SPI时钟频率为10 MHz、AD9361芯片的系统时钟更改设置为40 MHz、初始化过程中输出端频率设置为1.4 GHz、DQPSK的解调采用点积叉积方式进行解调4种方法予以解决;实验结果表明4个相关问题解决效果良好,所实现的DQPSK收发性能可靠。 相似文献
23.
This paper describes and validates by comparisons with tests a one‐zone model for computing temperature of fully developed compartment fires. Like other similar models, the model is based on an analysis of the energy and mass balance assuming combustion being limited by the availability of oxygen, ie, a ventilation‐controlled compartment fire. However, the mathematical solution techniques in this model have been altered. To this end, a maximum fire temperature has been defined depending on combustion efficiency and opening heights only. This temperature together with well‐defined fire compartment parameters was then used as a fictitious thermal boundary condition of the surrounding structure. The temperature of that structure could then be calculated with various numerical and analytical methods as a matter of choice, and the fire temperature could be identified as a weighted average between the maximum fire temperature and the calculated surface temperature of the surrounding structure as a function of time. It is demonstrated that the model can be used to predict fire temperatures in compartments with boundaries of semi‐infinitely thick structures as well as with boundaries of insulated and noninsulated steel sheets where the entire heat capacity of the surrounding structure is assumed to be concentrated to the steel core. With these assumptions, fire temperatures could be calculated with spreadsheet calculation methods. For more advanced problems, a general finite element solid temperature calculation code was used to calculate the temperature in the boundary structure. With this code, it is possible to analyze surrounding structures of various kinds, for example, structures comprising several materials with properties varying with temperature as well as voids. The validation experiments were accurately defined and surveyed. In all the tests, a propane diffusion burner was used as the only fire source. Temperatures were measured with thermocouples and plate thermometers at several positions. 相似文献
24.
25.
《International Journal of Hydrogen Energy》2020,45(3):2257-2278
The uniform temperature distribution of a cross-flow planar solid oxide fuel cell (SOFC) stack plays an essential role in stack thermal safety and electrical property. However, because of the strict requirements in stack sealing struture, it is hard to acquire the temperature inside the stack using thermal detection devices within an acceptable cost. Therefore, accurately estimating the two-dimensional (2-D) temperature distribution of the cross-flow stack is crucial for its thermal management. In this paper, Firstly, a 2-D mechanism model of a cross-flow planar SOFC stack is established. The stack is divided into 5*5 nodes along the gas flow directions, which can reflect the stack states with moderate computational burden. Then, experimental test data is utilized to modify and validate the stack model, guaranteeing the model accuracy as well as the reliability of model-based state estimator design. Finally, easily-measured stack inputs and outputs are selected, and a temperature distribution estimator combined with unscented kalman filter (UFK) approach is developed to achieve accurate and fast temperature distribution estimation of a cross-flow SOFC stack. Simulation results demonstrate that the UKF-based temperature distribution estimator can precisely and quickly achieve the temperature distribution estimation of the cross-flow stack under both static state and dynamic state changes and is applicable to cross-flow stacks with different size or cell number as well, the maximum estimated absolute error is less than 0.15 K with an absolute error rate of 0.015%, which indicates the developed estimator has good estimation performances. 相似文献
26.
Erfan Khodabandeh Hesam Moghadasi Mohsen Saffari Pour Mikael Ersson P r G. J nsson Marc A. Rosen Alireza Rahbari 《中国化学工程学报》2020,28(4):1029-1038
This research investigates a numerical simulation of swirling turbulent non-premixed combustion. The effects on the combustion characteristics are examined with three turbulence models: namely as the Reynolds stress model, spectral turbulence analysis and Re-Normalization Group. In addition, the P-1 and discrete ordinate (DO) models are used to simulate the radiative heat transfer in this model. The governing equations associated with the required boundary conditions are solved using the numerical model. The accuracy of this model is validated with the published experimental data and the comparison elucidates that there is a reasonable agreement between the obtained values from this model and the corresponding experimental quantities. Among different models proposed in this research, the Reynolds stress model with the Probability Density Function (PDF) approach is more accurate (nearly up to 50%) than other turbulent models for a swirling flow field. Regarding the effect of radiative heat transfer model, it is observed that the discrete ordinate model is more precise than the P-1 model in anticipating the experimental behavior. This model is able to simulate the subcritical nature of the isothermal flow as well as the size and shape of the internal recirculation induced by the swirl due to combustion. 相似文献
27.
Amir Mowla Mehrez Agnaou Tanyakarn Treeratanaphitak Hector M. Budman Nasser M. Abukhdeir Marios A. Ioannidis 《American Institute of Chemical Engineers》2020,66(6):e16959
We quantify the ability of the two-fluid Euler–Euler model to predict the overall gas hold-up during two-phase flow in vertical columns using a combination of experiments and simulations. Gas hold-up in a bubble column and gas hold-up in the less-frequently studied co-current flow are investigated. For homogeneous flow characterized by nearly uniform bubble size, Euler–Euler model predictions are within 10% of the experimental values for both modes of operation, if the bubble diameter supplied as input to the model is the average bubble diameter in the physical system. This also holds true for heterogeneous flow in bubble columns despite the presence of a broad distribution of bubble sizes, if turbulence and bubble swarm effects on momentum exchange between phases are properly accounted for. Swarm corrections adequate for bubble columns, are less successful for co-current heterogeneous flow, for which gas hold-up predictions are least accurate (average error of 22%). 相似文献
28.
《中国有色金属学会会刊》2020,30(8):2170-2176
To clarify the influence of the deformation texture on the mechanical properties, pure Mo plates were processed by various cross rolling procedures, and the relation among texture, microstructure and mechanical properties was discussed. The results show that cross rolling of the Mo plates is beneficial for the formation of the rotated cube component, i.e., {001}〈110〉. The corresponding orientation density exhibits a positive correlation with the total rolling deformation and the current-pass deformation. When the total deformation is 96% or greater, the Mo plates form a texture orientation dominated by {001}〈110〉, whereas the γ-fibre texture becomes weaker and the cube texture {100}〈100〉 disappears completely. The presence of {001}〈110〉 has great effects on the properties of cross-rolled Mo plates, which is beneficial for strength enhancement and plasticity reduction in both the rolling direction (RD) and the transverse direction (TD). 相似文献
29.
30.
Iqra Jabeen Asma Ejaz Adeel Akram Yasar Amin Jonathan Loo Hannu Tenhunen 《国际射频与微波计算机辅助工程杂志》2019,29(11)
A miniaturized, polarization insensitive, and fully passive chipless radio frequency identification tag is proposed in this research article. The realized tag is based on slotted elliptical structures in a nested loop fashion with identical lengths and widths of slot resonators. Alteration of data sequence is accomplished by addition and elimination of nested resonators in the geometric structure. The tag is capable to encode 10 bits of data and covers spectral range from 3.6 to 15.6 GHz. The formulated structure demonstrates polarization insensitive characteristic. The data encoding structure is analyzed and optimized for different substrates that are, Rogers RT/duroid/5880, Rogers RT/duroid/5870, and Taconic TLX‐0 over the miniaturized footprint of 22.8 × 16 mm2. The presented tag is robust, novel, compact, and flexible exhibiting a stable response to impinging electromagnetic waves at various angles of incidence. 相似文献